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Appendix VI.

1141

eccentric crank join A! BJ. and divide it proportionately to A c B.
Then R is the crank required. For, drawing parallels D GJ E Cj;
o D is the crank that would give the proper fraction of A'S motion
at c, while OE acts similarly for B. Hence, by Fig. 1007, the
final crank is o GV

McFarlane   Gray   has   given   another  rule.      Referring to
Fig. 1010,

Let OK

B D  BC

D E  2

and with radius o K draw the arc B c.    In B c take point K such
that

DF

FE

BK
KC

Then A K is the virtual or equivalent crank.     If the rods are
crossed make the arc B c convex to A.

Correct graphic solution:   The method of equivalent crank
can only be used for first approximation.    The proportions of the